Intelligent transportation systems (ITS) are configured to automate interactions between vehicles in order to achieve greater levels of safety, security and efficiency. For example, an ITS may enable a mobile terminal on an emergency vehicle to notify surrounding vehicles and/or upcoming traffic of its approach. Advantageously the notification may cause an alert and may even attempt to slow the nearby vehicles to allow for the safe passage of the emergency vehicle. Other embodiments of an ITS may include setting variable speed limits, reporting traffic flow and/or the like.
In order to provide wireless access in vehicular environments, a Wireless Access Vehicular Environment (WAVE) system architecture was developed. A WAVE system consists of fixed road side units (RSUs) usually positioned along roads and mobile terminals (e.g., on board units or OBUs) mounted in vehicles The RSUs and mobile terminals may form WAVE basic service sets (WBSSs) connected to the Wide Area Network (WAN) via an appropriate portal. Such a portal may be implemented via cable linking the RSU and the WAN, but this may, for example, add significantly to cost of implementing an ITS system. Another version of a WAVE system may be implemented wirelessly over an ITS band, However, using the wireless band has proven, for example, to starve an ITS-Dedicated Short Range Communications (DSRC) system of frequency resources. The ITS-DSRC is customarily deployed over 75 MHz of bandwidth in a relatively high-frequency band around 5.9 GHz in 10-20 MHz channel bandwidth, and therefore may not be suited for potentially long transmission range due to path loss. Additionally, increasing transmission power of the RSU-WAN link to account for the transmission range may lead to significant interference issues for the RSU-mobile terminal link. Other current wireless solutions, such as those solutions used in current cellular networks are generally not suitable for an ITS environment due to the potential speed and high mobility of a mobile terminal as well as the generally small size of some RSU cells.